class Solution {
    bool vis[21][21];
    int dx[4]={1,-1,0,0};
    int dy[4]={0,0,1,-1};
    int ret;
    int m,n,step;
public:
    int uniquePathsIII(vector<vector<int>>& grid) {
        m=grid.size(),n=grid[0].size();
        int bx=0,by=0;
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(grid[i][j]==0)step++;
                else if(grid[i][j]==1)bx=i,by=j;
            }
        }
        step+=2;
        vis[bx][by]=true;
        dfs(grid,bx,by,1);
        return ret;
        
    }

    void dfs(vector<vector<int>>& grid,int i,int j,int count)
    {
        if(grid[i][j]==2){
            if(count==step)ret++;
            return;
        }
        for(int k=0;k<4;k++)
        {
            int x=i+dx[k],y=j+dy[k];
            if(x>=0 && x<m && y>=0 && y<n
            && grid[x][y]!=-1 && !vis[x][y])
            {
                vis[x][y]=true;
                dfs(grid,x,y,count+1);
                vis[x][y]=false;
            }
        }
        
    }
};
